Gram-negative bacteria have an outer membrane composed of a lipid bilayer, which does not exist in Gram-positive bacteria, and therefore tend to have stronger drug resistance, as compared to Gram-positive bacteria. Gram-negative bacteria are also known to have a plurality of drug efflux proteins, which are involved in drug resistance (Antimicrobial Resistance, 2002, Mar. 1, 34, pp. 634-640).
Among Gram-negative bacteria, Pseudomonas aeruginosa, in particular, has a strong tendency to show intrinsic resistance to various antimicrobial substances. In recent years, Pseudomonas aeruginosa which has gained resistance to carbapenem drugs, quinolone drugs, aminoglycoside drugs, or the like has been often isolated in medical settings (J. Antimicrob. Chemother., 2003, Vol. 51, pp. 347-352). Moreover, multi-drug resistant Pseudomonas aeruginosa has been isolated (Jpn. J. Antibiotics, 2006, Vol. 59, No. 5, pp. 355-363) and has posed worldwide major problems.
Multidrug resistant bacteria not only exhibit resistance to a plurality of antimicrobial substances, but also have the problem of limiting applicable antimicrobial substances. Thus, in addition to development of new medicaments, combination use with an existing antimicrobial substance is an important option. However, the theory of combination therapy directed against resistant bacteria has not been established, and satisfactory therapeutic effects have not been necessarily achieved (Kagaku Ryoho No Ryoiki, 2012, Vol. 28, No. 9).
UDP-3-O-acyl-N-acetylglucosamine deacetylase (LpxC) is an enzyme in charge of the synthesis of lipid A (the hydrophobic anchor of LPS, which is the constituent of the outer membrane).
Lipid A biosynthesis consists of reactions in 10 stages, and LpxC catalyzes the second stage to remove the acetyl group of UDP-3-O-acyl-N-acetylglucosamine (J. Biol. Chem., 1995, Vol. 270, pp. 30384-30391). Lipid A is a component essential for the formation of the outer membrane, and is indispensable for the survival of Gram-negative bacteria (J. Bacteriol., 1987, Vol. 169, pp. 5408-5415). LpxC is one of the rate-determining important enzymes during the process of lipid A biosynthesis, and is an indispensable enzyme for lipid A biosynthesis. Thus, a drug inhibiting the activity of LpxC is highly expected to be capable of becoming an antimicrobial agent effective against Gram-negative bacteria including Pseudomonas aeruginosa, particularly against drug resistant Pseudomonas aeruginosa, because such a drug has a mechanism of action different from those of conventional drugs.
Compounds having LpxC inhibitory activity have been known so far (Patent Documents 1 to 7).